Members of the human nuclear hormone receptor (NR) superfamily serve as receptors for steroids, thyroid hormones, retinoids, oxysterols, fatty acids, and bile acids. Nearly all of the NRs with identified ligands have been successful targets for drugs treating a variety of diseases including diabetes, dyslipidemia, inflammation, and cancer. FXR is a NR that functions as a physiological receptor for bile acids. FXR plays a critical role in bile acid homeostasis as well as glucose and lipid metabolism. FXR has been implicated as a drug target for the treatment of dyslipidemia (atheroscelerosis), diabetes, and gallstones. Although a few synthetic agonists have been identified for FXR, no selective antagonists have yet been characterized. Thus, the chemical tools available to characterize this receptor are limited. The proposed research is focused on development of assays to identify FXR antagonists that can be used as chemical tools to fully characterize the biological function of FXR as well as to validate this receptor as a potential drug target. In order to develop the assays required for identification of FXR antagonists the following specific aims will be addressed: (1) Develop and validate a biochemical assay to detect FXR antagonists in a high-throughput screen format.;(2) Develop and validate secondary assays for the purpose of characterizing antagonist "hits" identified in an FXR high throughput screen;and (3) Perform a validating screen of the FXR assay flow scheme using the LOPAC 1280 chemical library. PUBLIC HEALTH RELEVANCE: This proposal focuses on development of screening assays to identify specific FXR antagonists. FXR is a nuclear receptor that functions as a physiological receptor for bile acids. No selective FXR antagonists currently exist and identification of antagonists will allow for characterization of the role of this receptor in regulation of metabolism.